1. Field of the Invention
This invention generally relates to aircraft manufacturing and particularly relates to locking fasteners used to fasten an aircraft frame member to another frame member.
2. Description of the Prior Art
Aircraft fuselages are typically assembled by constructing a metal frame structure from beams and attaching panels to the outside of the frame. The frame gives rigidity and strength to the aircraft, and the panels form an enclosure to provide a streamlined outer surface to reduce aerodynamic drag and to protect the components carried within the frame from the exterior environment. The panels are may be riveted or adhered to the frame.
A second method of constructing a fuselage is to machine the fuselage, or a portion thereof, from a solid block of metal. The fuselage comprises strengthening members that obviate the need for a separate frame. Holes in the fuselage are provided to lighten the fuselage and to allow access to internal components of the aircraft after assembly. These holes are covered by panels affixed to the fuselage.
Composite materials are used to construct sections of aircraft, but the use has generally been limited to wing surfaces and exterior panels. Methods of construction which would provide integral frame members and limit the number of joints in a composite fuselage would allow for cost-effective manufacturing of strong, light aircraft. However, fasteners are needed to extend through the entire height of the frame members. These fasteners need to be of a locking type to prevent their loosening, which could allow the sections of the fuselage to move relative to one another and result in a catastrophic failure of the aircraft.
A fastener is provided for constructing a fuselage of an aircraft, the fastener having male and female sections. Each section has an elongate portion and a head having an outer diameter that is larger than the diameter of the elongate portion. The elongate portion of the male section is a cylindrical shaft having external threads. The elongate portion of the female section is a tubular member having internal threads for engaging the threads of the male section. The outer end of the threaded portion of the male section is castellated and has a threaded cavity.
The head of each of the male and female sections has a high-torque connector profile for receiving a tool used to tighten the sections together. The head of the female section also has a hole through the center of the head that opens into the center of the female elongate portion, the hole aligning with the center of the castellated portion of the male portion. A tapered, threaded lock screw is inserted into the hole and rotated to cause the threads to engage the interior of the castellated portion of the male section. The segments of the castellated portion are moved radially outward by the taper of the lock screw, causing a large normal force between the threads on the segments and the threads of the female portion. This force results in a large frictional force, preventing relative rotation between the male and female sections.